Synthetic resins, halogen-containing resins in particular, are unstable against heat and light and may deteriorate with time or deteriorate during a crosslinking reaction or a molding process. Hence, a lead compound, an organotin compound, and a Cd/Ba-, Ba/Zn- or Ca/Zn-based composite organic acid salt have been used as a stabilizer therefor. However, the toxicity of these stabilizers and environmental pollution caused by these stabilizers have started to be acknowledged as problems. Therefore, various stabilizers comprising calcium hydroxide which is safer and less expensive as a main component have been developed for synthetic resins (refer to Patent Publications 1 and 2).
However, since the solubility of quick lime in water is high, calcium hydroxide is apt to undergo crystal growth, has a small specific surface area (refer to Patent Publication 3) and is limited in halogen capturing capability. Further, when a calcium hydroxide based stabilizer is added to a synthetic resin, the resulting synthetic resin has problems of poor thermal stability and very poor initial colorability as compared with when a lead compound or an organotin compound is added to a synthetic resin.
Despite these problems, since calcium hydroxide has excellent safety and is inexpensive, it is expected to be used as a stabilizer for a synthetic resin, and an improvement thereof has been desired.    (Patent Publication 1) JP-A 6-316662 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)    (Patent Publication 2) JP-A 11-193336    (Patent Publication 3) JP-A 2001-123071